Simulation of AFM

Development of new technologies often hinges around the creation of new materials, or, in the case of nanotechnology, the precise engineering of structures composed of relatively few atoms. To understand the connection between materials and their functionality we need to know their detailed atomic structure. This includes the nature of any defects that are present since such imperfections are often responsible for or change the property that makes the material useful. While there are many techniques that can probe the structure of solids with atomic resolution, such as X-ray and neutron diffraction, many of these methods only “see” the bulk average over many atoms and so the exciting regions for chemistry, namely the surfaces and defects, are largely invisible. In contrast, atomic force microscopy (AFM) is an imaging technique that promises to deliver resolution of individual atoms on surfaces and therefore, in principle, is capable of observing defects. However, the act of imaging the surface is sensitive to not only the details of the surface itself, but also any solution that lies above it, as well as the nature of the probe that is used to scan the atoms. In light of this, the crucial questions are what are we actually observing when we see something with “atomic resolution” in AFM and can we really detect single atom defects?

The primary aim of this project is to combine state-of-the-art experimental AFM techniques with computer simulations that are capable of generating AFM images in-silico in order to answer the above question. Our ability to harness the potential of AFM for many applications in areas such as nanoscience and crystal engineering hinges on being able to correctly interpret these images.

Ion vacancies in the surface of the mineral calcite can be identified by comparison with simulations of the AFM image based on atomistic molecular dynamics. See B. Reischl, P. Raiteri, J. D. Gale, and A. L. Rohl. 2016. “Can Point Defects in Surfaces in Solution be Atomically Resolved by Atomic Force Microscopy?.“ Physical Review Letters, 117.

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